Problem: Simplify the following expression: $x = \dfrac{k^2 - 3k - 18}{k + 3} $
Answer: First factor the polynomial in the numerator. $ k^2 - 3k - 18 = (k + 3)(k - 6) $ So we can rewrite the expression as: $x = \dfrac{(k + 3)(k - 6)}{k + 3} $ We can divide the numerator and denominator by $(k + 3)$ on condition that $k \neq -3$ Therefore $x = k - 6; k \neq -3$